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<div class="refentry">
<a name="boost.proto.make.impl"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Struct template impl</span></h2>
<p>boost::proto::make::impl</p>
</div>
<h2 class="refsynopsisdiv-title">Synopsis</h2>
<div class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../../proto/reference.html#header.boost.proto.transform.make_hpp" title="Header &lt;boost/proto/transform/make.hpp&gt;">boost/proto/transform/make.hpp</a>&gt;

</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <a class="link" href="../../../Expr.html" title="Concept Expr">Expr</a><span class="special">,</span> <span class="keyword">typename</span> State<span class="special">,</span> <span class="keyword">typename</span> Data<span class="special">&gt;</span> 
<span class="keyword">struct</span> <a class="link" href="impl.html" title="Struct template impl">impl</a> <span class="special">:</span> <span class="keyword"></span> <a class="link" href="../transform_impl.html" title="Struct template transform_impl">proto::transform_impl</a><span class="special">&lt;</span> <span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">State</span><span class="special">,</span> <span class="identifier">Data</span> <span class="special">&gt;</span> <span class="special">{</span>
  <span class="comment">// <a class="link" href="impl.html#boost.proto.make.impltypes">types</a></span>
  <span class="keyword">typedef</span> <span class="emphasis"><em><span class="identifier">see</span><span class="special">-</span><span class="identifier">below</span></em></span> <a class="link" href="impl.html#boost.proto.make.impl.result_type"><span class="identifier">result_type</span></a><span class="special">;</span>

  <span class="comment">// <a class="link" href="impl.html#id-1_3_31_5_50_2_1_3_5_4-bb">public member functions</a></span>
  <span class="identifier">result_type</span> <a class="link" href="impl.html#id-1_3_31_5_50_2_1_3_5_4_1-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">expr_param</span><span class="special">,</span> 
                         <span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">state_param</span><span class="special">,</span> 
                         <span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">data_param</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="id-1.3.31.5.52.6.4.4.4"></a><h2>Description</h2>
<div class="refsect2">
<a name="id-1.3.31.5.52.6.4.4.4.2"></a><h3>
<a name="boost.proto.make.impltypes"></a><code class="computeroutput">impl</code> 
        public
       types</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<p>
<span class="keyword">typedef</span> <span class="emphasis"><em><span class="identifier">see</span><span class="special">-</span><span class="identifier">below</span></em></span> <a name="boost.proto.make.impl.result_type"></a><span class="identifier">result_type</span><span class="special">;</span></p>
<p>
                <code class="computeroutput"><a class="link" href="../make.html" title="Struct template make">proto::make</a>&lt;T&gt;::impl&lt;Expr, State, Data&gt;::result_type</code> is
                computed as follows:
              </p>
<p>
                If <code class="computeroutput">T</code> is an <a class="link" href="../../../ObjectTransform.html" title="Concept ObjectTransform">ObjectTransform</a> of the form
                <code class="computeroutput">Object(A<sub>0</sub>,…A<sub>n</sub>)</code> or
                <code class="computeroutput">Object(A<sub>0</sub>,…A<sub>n</sub> ...)</code>,
                then let <code class="computeroutput">O</code> be the return type
                <code class="computeroutput">Object</code>. Otherwise, let <code class="computeroutput">O</code>
                be <code class="computeroutput">T</code>. The <code class="computeroutput">result_type</code> typedef is
                then computed as follows:
              </p>
<p>
                </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
                      If <code class="computeroutput"><a class="link" href="../is_transform.html" title="Struct template is_transform">proto::is_transform</a>&lt;O&gt;::value</code> is
                      <code class="computeroutput">true</code>, then let the result type be
                      <code class="computeroutput">
                        boost::result_of&lt;<a class="link" href="../when.html" title="Struct template when">proto::when</a>&lt;<a class="link" href="../_.html" title="Struct _">_</a>, O&gt;(Expr, State, Data)&gt;::type
                      </code>.
                      Note that a substitution took place.
                    </p></li>
<li class="listitem">
                    If <code class="computeroutput">O</code> is a template like
                    <code class="computeroutput"><a class="link" href="../noinvoke.html" title="Struct template noinvoke">proto::noinvoke</a>&lt;S&lt;X<sub>0</sub>,…X<sub>n</sub>&gt; &gt;</code>,
                    then the result type is calculated as follows:
                    <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem"><p>
                          For each <code class="computeroutput">i</code> in
                          <code class="computeroutput">[0,n]</code>, let <code class="computeroutput">
                            X<sub>i</sub>'
                          </code> be
                          <code class="computeroutput">
                            boost::result_of&lt;<a class="link" href="../make.html" title="Struct template make">proto::make</a>&lt;X<sub>i</sub>&gt;(Expr, State, Data)&gt;::type
                          </code>
                          (which evaluates this procedure recursively). Note that a substitution took place. (In this case,
                          Proto merely assumes that a substitution took place for the sake of compile-time efficiency. There
                          would be no reason to use <code class="computeroutput"><a class="link" href="../noinvoke.html" title="Struct template noinvoke">proto::noinvoke&lt;&gt;</a></code>
                          otherwise.)
                        </p></li>
<li class="listitem"><p>
                          The result type is
                          <code class="computeroutput">
                            S&lt;X<sub>0</sub>',…X<sub>n</sub>'&gt;
                          </code>.
                        </p></li>
</ul></div>
</li>
<li class="listitem">
                    If <code class="computeroutput">O</code> is a template like
                    <code class="computeroutput">S&lt;X<sub>0</sub>,…X<sub>n</sub>&gt;</code>,
                    then the result type is calculated as follows:
                    <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem"><p>
                          For each <code class="computeroutput">i</code> in
                          <code class="computeroutput">[0,n]</code>, let <code class="computeroutput">
                            X<sub>i</sub>'
                          </code> be
                          <code class="computeroutput">
                            boost::result_of&lt;<a class="link" href="../make.html" title="Struct template make">proto::make</a>&lt;X<sub>i</sub>&gt;(Expr, State, Data)&gt;::type
                          </code>
                          (which evaluates this procedure recursively). Note whether any substitutions took place during
                          this operation.
                        </p></li>
<li class="listitem"><p>
                          If any substitutions took place in the above step and
                          <code class="computeroutput">
                            S&lt;X<sub>0</sub>',…X<sub>n</sub>'&gt;
                          </code> has a nested
                          <code class="computeroutput">type</code> typedef, the result type is
                          <code class="computeroutput">
                            S&lt;X<sub>0</sub>',…X<sub>n</sub>'&gt;::type
                          </code>.
                        </p></li>
<li class="listitem"><p>
                          Otherwise, the result type is
                          <code class="computeroutput">
                            S&lt;X<sub>0</sub>',…X<sub>n</sub>'&gt;
                          </code>.
                        </p></li>
</ul></div>
</li>
<li class="listitem">
                    Otherwise, the result type is <code class="computeroutput">O</code>, and note that no
                    substitution took place.
                  </li>
</ul></div>
<p>
              </p>
<p>
                Note that <code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">proto::when&lt;&gt;</a></code> is implemented
                in terms of <code class="computeroutput"><a class="link" href="../call.html" title="Struct template call">proto::call&lt;&gt;</a></code>
                and <code class="computeroutput"><a class="link" href="../make.html" title="Struct template make">proto::make&lt;&gt;</a></code>, so the
                above procedure is evaluated recursively.
              </p>
</li></ol></div>
</div>
<div class="refsect2">
<a name="id-1.3.31.5.52.6.4.4.4.3"></a><h3>
<a name="id-1_3_31_5_50_2_1_3_5_4-bb"></a><code class="computeroutput">impl</code> public member functions</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><span class="identifier">result_type</span> <a name="id-1_3_31_5_50_2_1_3_5_4_1-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">expr_param</span> expr<span class="special">,</span> 
                       <span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">state_param</span> state<span class="special">,</span> 
                       <span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">data_param</span> data<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<p>
                  <code class="computeroutput">
                    <code class="computeroutput"><a class="link" href="../make.html" title="Struct template make">proto::make</a></code>&lt;T&gt;::impl&lt;Expr,State,Data&gt;::operator()
                  </code>
                  behaves as follows:
                </p>
<p>
                  </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
                        If <code class="computeroutput">T</code> is of the form
                        <code class="computeroutput">O(A<sub>0</sub>,…A<sub>n</sub>)</code>, then:
                      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
                            If <code class="computeroutput">
                              <code class="computeroutput"><a class="link" href="../is_aggregate.html" title="Struct template is_aggregate">proto::is_aggregate</a></code>&lt;result_type&gt;::value
                            </code> is <code class="computeroutput">true</code>, then construct
                            and return an object <code class="computeroutput">that</code> as follows:
                            </p>
<pre class="programlisting">result_type that = {
  <code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">proto::when</a></code>&lt;<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, A<sub>0</sub>&gt;()(expr, state, data),
  …
  <code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">proto::when</a></code>&lt;<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, A<sub>n</sub>&gt;()(expr, state, data)
};</pre>
<p>
                          </p>
</li>
<li class="listitem">
<p>
                            Otherwise, construct
                            and return an object <code class="computeroutput">that</code> as follows:
                            </p>
<pre class="programlisting">result_type that(
  <code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">proto::when</a></code>&lt;<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, A<sub>0</sub>&gt;()(expr, state, data),
  …
  <code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">proto::when</a></code>&lt;<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, A<sub>n</sub>&gt;()(expr, state, data)
);</pre>
<p>
                          </p>
</li>
</ul></div>
</li>
<li class="listitem">
<p>
                        If <code class="computeroutput">T</code> is of the form
                        <code class="computeroutput">O(A<sub>0</sub>,…A<sub>n</sub> ...)</code>,
                        then let <code class="computeroutput">T'</code> be <code class="computeroutput">O(A<sub>0</sub>,…A<sub>n-1</sub>, <em class="replaceable"><code>S</code></em>)</code>,
                        where <em class="replaceable"><code>S</code></em> is a type sequence computed from the unpacking expression <code class="computeroutput">A<sub>n</sub></code>
                        as described in the reference for <code class="computeroutput"><code class="computeroutput"><a class="link" href="../pack.html" title="Struct pack">proto::pack</a></code></code>. Then, return:
                        </p>
<pre class="programlisting">proto::make&lt;T'&gt;()(expr, state, data)</pre>
<p>
                      </p>
</li>
<li class="listitem">
<p>
                        Otherwise, construct and return an object <code class="computeroutput">that</code>
                        as follows: </p>
<pre class="programlisting">result_type that = result_type();</pre>
<p>
                      </p>
</li>
</ul></div>
<p>
                </p>
</li></ol></div>
</div>
</div>
</div>
<div class="copyright-footer">Copyright © 2008 Eric Niebler<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div>
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